---------------------------------------------------
Arnfield clock with hour, minute, and seconds hands
---------------------------------------------------

------------------
Layout constraints
------------------

- aesthetics
  - individual dials for hours, minutes, and seconds
  - dial centers arranged in vertical line
  - minutes dial centered on clock face
  - hours and seconds dials equidistant from center (minutes axle)
  - hours dial on top, minutes dial on bottom

- 5 gear reductions required in order that all dials turn in proper direction (clockwise)

- excapement arms must be mounted on rear of clock 
  - if mounted on front, escapement arm A blocks seconds axle

- pendulum must be mounted on front of clock
  - if mounted on rear, pendulum rod will strike rewinder box

- pendulum rod must be mounted on hoop-shaped hanger
  - if hung straight down, pendulum rod will block seconds axle

-----------------
Gear calculations
-----------------
  
  Wheels and pinions as meshing pairs
  -----------------------------------

     a=12 b=60
     c=12 d=90
     e=12 f=96
     g=28 h=84
     i=20 j=80

  Wheels and pinions as printable units
  -------------------------------------

     STAR      sa   6:12   CCW
                     /
     SECONDS   bc  60:12   CW
                     /
               de  90:12   CCW
                     /
     MINUTES   fg  96:28   CW
                     /
               hi  84:20   CCW
                     /
     HOURS     j   80      CW

  Gear speeds
  -----------

     given:
          1 pendulum swing = 2 seconds

     then:
          a  turns 6 steps per rev * 1 swing per step * 2 seconds per swing = 12 seconds per rev = 5     rev per minute (STAR)
          bc turns 5 * (12 / 60)                                                                 = 1     rev per minute (SECONDS)
          de turns 5 * (12 / 60) * (12 / 90)                                                     = .13   rev per minute
          fg turns 5 * (12 / 60) * (12 / 90) * (12 / 96)                                         = .017  rev per minute  = 1   rev per hour (MINUTES)
          hi turns 5 * (12 / 60) * (12 / 90) * (12 / 96) * (28 / 84)                             = .0055 rev per minute = .33  rev per hour = 8 rev per day
          j  turns 5 * (12 / 60) * (12 / 90) * (12 / 96) * (28 / 84) * (20 / 80)                 = .0014 rev per minute = .083 rev per hour = 2 rev per day (HOURS)

  Weight drop
  ------------------------

   - 66 tooth sprocket mounted on minutes wheel
   - sprocket diameter = 76 mm
   - weight drop per rev = sprocket circumference / 2        <== divide by 2 because of pulley system
                         = 3.14 * 76 / 2
                         = 119 mm per rev
   - sprocket rev per hour = 1.0
   - weight drop per hour = sprocket rev per hour * weight drop per rev
                          = 1.0 * 119
                          = 119 mm
   - weight drop in 6 hours = 119 * 6 = 714 mm = 28 inches

-----------------
Gear construction
-----------------

- generate gear pair as dxf file using Rainer Hessmer's "Cycloidal Gear Builder"
  - original: www.hessmer.org/gears/CycloidalGearBuilder.html
  - local copy: ../cycloidal_gear_designer/webpage.htm

- import dxf file into blender 
  - gear outline will show up as a "curve" object

- Object mode
  - convert curve to mesh
- Edit mode
  - delete all edges except gear outline
  - select all edges
  - convert edges to face
  - extrude face 1mm
  - extruce again 2mm (for total thickness of 3 mm)
  - select lower edges
  - rescale them by .5mm radially
- Object mode
  - subtract center hole after displacing cylinder cutter by .0001 mm in Y direction to eliminate numerical problems
- Edit mode
  - select all faces
  - Mesh -> Normals -> Recalculate Outside

------
Prints 
------
  
  - cura slicer except for pendulum bob

  standard quality (.2mm layers)
  ------------------------------

    - frame
      - cc3d metallic silver
      - 210 C
      - 20% triangle infill

    - wall posts
      - cc3d metallic silver
      - 210 C
      - 100% infill

    - gears
      - hatchbox white
      - 100% infill
      - walls = 5
      - alternate extra wall = Y
      - z-seam = random
      - elephant foot compensation = -0.3

    - escapement arms and pendulum hanger
      - hatchbox white
      - 20% triangle infill
      - elephant foot compensation = -0.3

  super quality (.12mm layers)
  ----------------------------

    - sprocket
      - hatchbox white
      - 100% infill

    - star wheel and cap
      - hatchbox white
      - 20% triangle infill

  pendulum bob 
  ------------
  
  - 75mm diameter
  - copied from ../number_one/arnfield_number_one_247.blend
  - prusa slicer
  - cc3d metallic silver
  - super quality (.12 layers)
  - fill density = 100%
  - fill type = archimedian chords
  - top fill pattern = archimedian chords
  - seam position = rear
  - print time = 4 h
  - print twice (once for each side) and glue together

---------------
Post processing
---------------

- ream bearing holes using   #8  drill bit (4.98mm)
- drill out axle holes using #48 drill bit (1.90mm)

--------
Hardware
--------

  ---------------------
  5x2x2.5 ball bearings
  ---------------------

  - (12) gear axles
  - (4)  arm axles
  - (2)  pendulum axle
  - (2)  pulleys

  ---------------
  M1.9 steel rods
  ---------------
  
  - gear and escapement arm axles
  
    axle     length(mm)
    ----     ---------
    a           49
    bc fg j     63
    de hi       35
    A           15
    B           15
    C           15
    pendulum    20

  ------------
  M4 steel rod
  ------------
  
  - arm A stopper pin 12mm

  ------------
  M4x10 screws
  ------------

  - (6) frame post screws

  ----------------------------------------
  3mm OD x .5mm wall (2mm ID) brass tubing
  ----------------------------------------
  
  - axle sleeves

   axle       rear(mm) front(mm)
   ----       -------- ---------
    a          11          5
    bc          7          6
    de          8          9
    fg         2.5         5
    hi         16          1
    j          20          2
    pendulum   -           2
     
------
Tuning
------

- ensure tight fit of gears to hours, minutes, seconds, and star axles (otherwise dial hands won't stay aligned with gears)
- center up axial wheel to pinion alignments using brass sleeves
- adjust axial play by sliding bearings in/out until gears rattle slightly
- adjust primary weight until clock runs without stumbling
- adjust secondary weight to minimum amount that prevents ball chain from slipping/popping
- adjust position of pendulum bob to yield swing period of exactly 2 seconds

- ball chain:        48" long endless loop (96" total length)
- primary weight:   330 grams (subsequently increased to about 500g)
- secondary weight:  50 grams
- pendulum bob:      60 grams

--------
Rewinder
--------

- motor
  - $9 "Fielect Mini Gear Motor DC 6V 30RPM Micro Gear Motor, Speed Reduction Motor GA12-N20 for RC Car, Robot Model, DIY Engine Toys"
  - www.amazon.com/gp/product/B082GK16YJ
  - choose 6V 30 RPM version (380:1)

- small motor died (not enough torque)
  - replaced with (larger) JGY370 12V 30RPM worm gear motor similar to...
  - $15 www.amazon.com/Bringsmart-Turbine-Electric-Self-locking-JGY-370/dp/B07FD18SH2

